Tapered tubular implant formed from woven fabric

ABSTRACT

A tubular woven implantable graft having a tapered section is provided. The graft comprises a first diameter and a second diameter and has a generally constant number of warp yarns per inch adjacent both the first diameter and the second diameter. A method for producing an implantable woven graft is also provided. The method includes weaving a first section having a first diameter and a tapered diameter tapering from the first diameter to a second diameter. During weaving of the tapered section a number of warp yarns are dropped from the weave and compressive forces are applied to the fabric to narrow the width of the fabric.

RELATED APPLICATION

The present application claims priority to, and is a division of, U.S.application Ser. No. 13/752,494, filed Jan. 29, 2013 which claimspriority U.S. Provisional Patent Application No. 61/725,918 filed Nov.13, 2012. The entire description of the foregoing applications arehereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of woven implants. Inparticular the present invention relates to tubular woven materials thatare used to create prosthesis to be implanted into patients. Theimplants have particular application to the field of vascular implants.

BACKGROUND

Woven fabrics may be used during surgery to repair or replace variousdamaged or diseased lumens within the human body. A typical surgicalprocedure is vascular surgery in which a woven tubular prosthesis isused to repair a blood vessel. Grafts in which the lumen has a constantdiameter have been used successfully, however, problems have persistedin procedures in which the lumen diameter changes. In one application,the lumen tapers from a first diameter to a smaller second diameter. Inanother application, the lumen branches. In a branched application, theimplant may be formed by suturing together a number of separate lumens.Such a procedure is time consuming. Other known procedures of weavingbifurcated implants result in unacceptable seams and/or transitions.

Additionally, it is desirable to maintain a substantially consistentporosity in a woven implant. In particular, changes in porosity can leadto unacceptable voids or gaps in an implant that would require suturingduring the procedure to eliminate potential leakage through the wall ofthe implant.

SUMMARY OF THE INVENTION

In light of the foregoing, the present invention provides a method andapparatus for forming a woven tubular implant having one or more taperedor bifurcated sections. According to one aspect, the present inventionprovides a method for forming an implantable graft. The method comprisesthe steps of weaving a plurality of warp yarns including base yarns andsupplemental yarns. The textile includes a tapered section in which thewidth of the textile changes from a first width to a second width.During the process of weaving the tapered section, a plurality ofsupplemental yarns are dropped from the weaving process so that thenumber of ends per inch in the woven section adjacent the first width issimilar to the number of ends per inch in the woven section adjacent thesecond width. Additionally, during the weaving process, compressiveforces are applied to the width of the textile. After weaving thefabric, the dropped yarns protrude from the surface of the fabric.Accordingly, the protruding portions of the dropped yarns are trimmedfrom the fabric.

The present invention also provides an implantable woven graft thatincludes a first tubular section and a frustoconically shaped hollowtapered section. The first section comprises a woven fabric formed froma plurality of base yarns and a plurality of supplemental yarns. Thetapered section has a first diameter that is similar to the firstdiameter of the first tubular section. The tapered section is woven fromthe base yarns forming the first tubular section and a plurality of thesupplemental yarns. However, the supplemental yarns are dropped from theweave pattern in the tapered section so that ends of the supplementalyarns protrude from the surface of the tapered section. The protrudingyarns are spaced apart from one another around the circumference of thetapered section and the number of warp yarns per inch at the seconddiameter is similar to the number of warp yarns per inch at the firstdiameter.

DESCRIPTION OF THE DRAWINGS

The foregoing summary and the following detailed description of thepreferred embodiments of the present invention will be best understoodwhen read in conjunction with the appended drawings, in which:

FIG. 1 is a side view of a tapered tubular graft;

FIG. 2 is an enlarged diagrammatic view of a weave pattern for a portionof the graft illustrated in FIG. 1;

FIG. 3 is an enlarged diagrammatic view of a weave pattern for a portionof the graft illustrated in FIG. 1

FIG. 4 is a weaving loom for weaving the graft illustrated in FIG. 1;

FIG. 5 is a side view of the graft of FIG. 1 illustrated on a mandrelfor heat forming the graft;

FIGS. 6A-6D is series of views of the graft of FIG. 1 illustrated on theloom of FIG. 4 as the tapered portion of the graft is woven;

FIG. 6A is a view of the loom with a reed in a lowered position;

FIG. 6B is a view of the loom with the reed raised from the position inFIG. 6A;

FIG. 6C is a view of the loom with the reed raised from the position inFIG. 6B;

FIG. 6D is a view of the loom with the reed raised from the position inFIG. 6C;

FIG. 7A is a diagram of the design set-up for weaving the graft of FIG.1;

FIG. 7B is a diagram of the design set-up for weaving the graft of FIG.1;

FIG. 8 is a diagram of the harness draw for weaving the graft of FIG. 1;and

FIG. 9 is a side view of a bifurcated tapered tubular graft.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings in general and to FIG. 1 specifically, awoven graft is designated generally 10. The graft 10 is a woven tubularfabric designed to be implanted into a mammalian body. In particular,the graft is designed to be implanted into a human patient. The graft 10includes a tapered section 20 in which the graft tapers from a firstdiameter to a second diameter. Specifically, in the present instance,the graft includes a first portion 12 having a first diameter and asecond portion 16 having a second diameter that is smaller than thefirst diameter. A tapered section 20 has a major diameter correspondingto the first diameter and a minor diameter corresponding to the seconddiameter so that the tapered section connects the first section 12 withthe second section 16 to provide a continuously woven tubular element.

As discussed further below, the graft 10 is formed so that the fabrichas substantially similar characteristics along the length of the graft.Specifically, the ends per inch of the warp yarns in the graft issubstantially similar in each section 12, 16, 20 of the graft. In thisway, features such as the porosity and flexibility of the graft, aresubstantially similar along the length of the graft.

The graft may be formed from any of a number of natural or syntheticfibers. More than one type of yarn may be used as warp yarns and thefill yarns may differ from the warp yarns. Additionally, more than onetype of fill yarn may be used. However, in the present instance, thesame material is used for all of the warp yarns and all of the fillyarns. The yarn may be monofilament or multi-filament. In the presentinstance, the fibers are polyester fibers, such as 1/40/27/12Z PETmulti-filament fibers.

The graft 10 is a seamless lumen formed as a flat woven tubular textile.The weave may be any of a variety of weaves, including, but not limitedto plain, basket and twill weaves. In the present instance, the graft 10is formed of a plain double cloth weave forming a flattened tubularstructure. The characteristics of the weave pattern may vary dependingupon the application for the graft 10. However, in the present instance,the graft 10 is formed so that the walls are substantially impermeableto fluid, so that the graft forms a lumen that is substantiallyfluid-tight along its length with an inlet 13 and an outlet 17. Forexample, when used in a vascular application, the walls of the graft aresubstantially impermeable to blood so that the graft forms a conduitpermitting the flow of blood along the axis 15 of the graft whileimpeding blood leakage through the sidewalls of the graft.

To provide a fluid-tight textile, the fabric comprises approximately150-350 ends per inch (“EPI”) at approximately 100-200 picks per inch(“PPI”) for each face. Since the flat woven tube comprises two faces,the total EPI for the graft is approximately 300-700 EPI atapproximately 200-400 PPI. More specifically, the fabric may compriseapproximately 200-300 EPI at 125-175 PPI for each face. In the presentinstance, the fabric comprises approximately 225-275 EPI atapproximately 150 PPI for each face.

Referring to FIG. 1, the graft 10 comprises two hollow generallycylindrical portions 12, 16 having different diameters and a taperedportion 20 connecting the two cylindrical portions. The tapered portion20 is a generally frustoconical hollow portion that tapers from themajor diameter of the first portion 12 to the minor diameter of thesecond portion 16. The length of the taper may vary depending on theapplication. Specifically, the ratio of the length of the taperedportion 20 to the change in diameter from the major diameter to theminor diameter may vary depending on the application.

Although the first portion 12 may taper, in the present instance thefirst portion is substantially cylindrical having a generally orsubstantially constant diameter along the length of the first portion.Transition 22 marks the beginning of the taper for the tapered section20. As discussed further below, during the process of weaving the graft10, a plurality of warp yarns are dropped from the fabric to reduce thenumber of ends in the reduced diameter portions of the graft. Dependingon the geometry of the tapered section, the dropped yarns may be droppedall at once or the yarns may be dropped in two or more groupings. Forinstance, in the present instance, the total number of dropped yarns issplit among three groups and the groups are dropped at different pointsof the weaving process.

The point along the length of the graft where the first group of warpsyarns is dropped is designated 24 in FIG. 1. As the graft continues totaper inwardly, the point along the length of the graft where the secondgroup of warp yarns is dropped is designated 26. Finally, after thegraft tapers further, the point along the length of the graft where thethird group of warp yarns is dropped is designated 28. The transitionpoint where the taper of the tapered section 20 discontinues isdesignated 30. Similar to the first section 12, the second section 16 ofthe graft may taper along its length at a taper different than the taperof the tapered section. However, in the present instance, the secondsection 16 is generally or substantially cylindrical so that thediameter of the second section remains substantially constant along itslength.

As shown in FIGS. 1 and 4, the groups of warp yarns dropped during theweaving process are regularly or semi-regularly spaced out across thewidth of the fabric as the fabric is woven. In this way, each group ofdropped yarns may form a ring of yarns circumscribing the graft. Thefirst group of yarns dropped at point 24 in FIG. 1 form the ring of warpyarns designated 67 in FIG. 4. The second group of yarns dropped atpoint 26 in FIG. 1 form the ring of warp yarns designated 65 in FIG. 4.The third group of yarns dropped at point 28 in FIG. 1 form the ring ofwarp yarns designated 63 in FIG. 4. As discussed further below, the warpyarns that are dropped during the weaving process are subsequentlytrimmed. For this reason, in FIGS. 1 and 4 the dropped yarns appear asrings of short fibers protruding from the surface of the graft.

Depending on the trimming process, the ends of the trimmed yarns may bevisible as shown in FIG. 4 or the ends may be trimmed so close that thetrimmed ends are barely perceptible. Either way, the graft has agenerally smooth exterior surface. Furthermore, none of the droppedyarns protrude into the interior of the graft. Accordingly, in thepresent instance, the surface of the interior wall is substantiallyconstant without surface irregularities along the entire length of thegraft, including the tapered section 20.

Referring to FIGS. 2-3, sections of the fabric of the graft aredesignated 40. In FIG. 2, a section of fabric is shown in the flat wovenform, as it is formed on the weaving machine. In FIG. 3, a section ofthe fabric is shown after the material is formed into a cylindricalconfiguration as discussed further below.

The fabric is a double weave fabric formed of a plurality of warp yarnsand weft yarns. The warp yarns of the front face are designated 52 andthe warp yarns of the rear face are designated 54 in FIGS. 2-3. The weftyarns of the front face are designated 70 and the weft yarns of the rearface are designated 72. The groups of dropped yarns are designated 60,with the warp yarns dropped from the front face designated 62 a and thewarp yarns dropped from the rear face designated 62 b

Method for Producing

Referring now to FIGS. 4-6D, the method for producing the graft will bedescribed in greater detail. The graft 10 is woven on a loom 100configured to produce a plain weave double cloth textile. The loom 100may be any of a variety of types, including, but not limited to ajacquard loom, a circular loom or a dobby loom. In the present instance,the graft is produced on a dobby loom 100. The loom 100 includes aplurality of harnesses 105 for controlling a plurality of heddles 125that control the warp yarns. In FIG. 4, the heddles are illustrated aswider than the actual heddles, and a smaller number is illustrated thanare used in forming the tapered sleeve described below.

Each harness controls a plurality of heddles 125 between a firstposition and a second position, such as a raised position and a loweredposition. The number of harnesses 105 may vary depending on the size andconfiguration of the graft. In the present instance, the loom utilizestwenty harnesses 105.

From the harnesses 105, the warp yarns pass through a reed 130 having aplurality of slots or dents 132. The reed 130 may be a straight reed ora tapered reed. In the present instance, the reed 130 is a tapered reedso that the reed tapers from a first width down to a second width thatis narrower than the first width. Specifically, the reed 130 is widestat the upper end of the reed and is narrowest at the lower end of thereed. In particular, the dents of the reed are spaced out across thewidth of the reed so that each dent is substantially the same width. Thedents 132 taper from the top of the reed to the bottom of the reed sothat the dents are widest at the top of the reed and narrowest at thebottom. Alternatively, the reed may be inverted so that the dents andthe reed are widest at the bottom and narrowest at the top.

The position of the reed is controlled by a controller that is operableto selectively move the reed up or down to vary the width of the wovenfabric. Specifically, moving the reed 130 upwardly pulls or squeezes thewarp yarns inwardly, increasing the ends per inch of the fabric if thenumber of warp yarns remains constant. Similarly, moving the reeddownwardly pulls the warp yarns outwardly decreasing the number of endsper inch of the fabric if the number of warp yarns remains constant. Thecontroller may control the timing and rate of reed movement depending ona number of variables, including, but not limited to: the configurationof the graft, the desired density and the number and timing of droppedwarp yarns.

The loom 100 also comprises one or more shuttles 135 for weaving theweft yarns 70, 72 onto the warp yarns 52, 54. When a single lumen graftis formed, such as the graft 10 illustrated in FIG. 1, a single shuttle135 may be used. When a multiple lumen graft is formed, such as thegraft 210 illustrated in FIG. 9, multiple shuttles may be used asdiscussed further below.

Each pass of the shuttle 135 across the warp yarns comprises a pick.When weaving a double cloth textile to form a tubular structure, a passof the shuttle back and forth completes two pick lines which form asingle continuous thread circumscribing the circumference of the tubularfabric. As the shuttle moves forward (left to right from the perspectiveof FIGS. 2-3), it weaves a pick line on the front face of the fabric. Asthe shuttle returns (right to left from the perspective of FIGS. 2-3),it weaves a pick line on the rear face of the fabric. By raising andlowering the warp yarns after each forward pass and return pass of theshuttle, the weft yarn from the shuttle continuously weaves from thefront face to the rear face without a break or seam.

After the shuttle 135 weaves the weft yarn, the loom moves the reed 130toward the fell to beat the fabric. The leading edge of the woven fabricis attached to a take-up roll so that the fabric is continuously woundonto the take-up roll as the fabric is finished. The take-up roll alsomaintains tension on the warp yarns so that the warp yarns are underappropriate tension to weave the fabric. For instance, the take-up rollmay be rotated regularly as the weaving process continues. As thetake-up roll rotates, the woven material is wound onto the take-up roll,thereby applying tension to the warp yarns.

As discussed above, to weave the fabric, a controller controls theoperation of the harnesses 105, the reed 130 and the shuttle(s) to weavethe fabric that forms the graft 10. For instance, in order to form adouble cloth weave with a tapered section, the yarns are drawn so that aplurality of base warp yarns extend through a plurality of harnesses.Base yarns are yarns that are woven with the weft yarns along the entirelength of the graft. At the same time, a plurality of dropped yarns aredrawn through a plurality of harnesses. The dropped yarns are woven withthe weft yarns for a portion of the graft and are dropped from the wovenfabric for a portion of the length of the graft.

For instance, referring to FIG. 1, the first section 12 of the graft iswoven by controlling the harnesses through which the base yarns anddropped yarns are drawn so that the weft yarns are woven among all orsubstantially all the base and dropped yarns. The tapered section 20 iswoven by controlling the base yarns and dropped yarns so that the weftyarns are woven among the base yarns, but not all of the dropped yarns.The pattern for dropping the yarns from the weave may vary depending onthe configuration of the taper and the desired characteristics of thewoven fabric. In particular, the position of the dropped yarns may becontrolled so that the dropped yarns are all removed from the weave atsubstantially the same time. Alternatively, the dropped yarns may beremoved gradually.

For example, the dropped yarns may be removed in groups. The totalnumber of dropped yarns may be divided into two or more groups ofdropped yarns. At a certain point along the length of the woven fabric,a first group of dropped yarns may be controlled so that the first groupof dropped yarns is not woven with the weft yarn. For example, referringto FIG. 1, the first group of dropped yarns may be dropped from theweave at point 24, the second group may be dropped at point 26 and thethird group may be dropped at point 28. This progression of droppedyarns is shown in FIGS. 6A-6D.

Referring to FIGS. 6A-D, the dropped yarns are spaced apart and extendacross the width of the fabric on both the front face (the face shown inFIGS. 6A-D) and the back face (the opposite face that is not visible inFIGS. 6A-D). In FIG. 6A, the fabric 10 is illustrated prior to any yarnsbeing dropped. FIG. 6B illustrated the fabric after a first group ofyarns is dropped. FIG. 6C illustrates the fabric after a second group ofyarns is dropped, so that both the first and second groups of droppedyarns are visible on the top surface of the fabric 10. Specifically, thefirst and second groups of dropped yarns are positioned so that thefirst and second groups of dropped yarns are not woven with the weftyarn as the shuttle 135 moves across the fabric. The process of droppinggroups of yarns may repeat until all of the dropped yarns are droppedfrom the weaving pattern. For example, the third and final group ofdropped yarns may be dropped from the weave at point 28 in FIG. 1. Thethird group of dropped yarns can be seen in FIG. 6D, along with thefirst and second group of yarns that were dropped earlier in theprocess.

After all of the dropped yarns are dropped from the weaving pattern, theweaving may continue weaving the base yarns. The result is a flat woventubular textile having three sections: (1) a first section 12 in whichthe base and dropped yarns are woven in the fabric; (2) a second section20 in which the dropped yarns are dropped from the weave; and (3) athird section 16 in which the base yarns are woven without the droppedyarns. In this way, the dropped yarns are interlaced with the weft yarnsin the first section 12, but are outside of the weave pattern in part ofthe tapered section 20 and are outside of the weave pattern in all ofthe third section 16. The result is a plurality of warp yarns that havea portion woven into the fabric and a portion unwoven. The unwovenportions extend outwardly from the surface of the fabric as shown inFIGS. 2-3, 6B-6D and 9.

As the tapered section 20 is woven, the reed may also be controlled toprovide a substantially uniform taper. For instance, referring to FIGS.1 and 6A-6D, the reed 135 may be moved as the weaving process of thetapered section 20 progresses. While the first portion 12 is beingwoven, the reed 130 may be lowered so that the reed and the dents 132are at their widest point for the weave, as shown in FIG. 6A. As theweave process progress, the reed 130 may be raised in a number of stepsor it may be raised in a continuous manner depending on the shape of thegraft.

In the present instance, the reed 130 is maintained in the loweredposition shown in FIG. 6A while the first section 12 of the graft iswoven. At transition point 22 shown in FIG. 1, the reed 130 begins beingraised to narrow the width of the fabric. While the tapered section 20is being woven, the reed 130 is progressively raised as shown in FIGS.6B-6D. The controller may control the position of the reed so that it israised at a uniform rate from the lowered position to the raisedposition. Alternatively, the controller may control the position of thereed so that the movement of the reed accelerates and decelerates as thegroups of warp yarns are dropped. In the present instance, thecontroller controls the position of the reed 130 so that the reed israised at a generally uniform rate. For example, the reed may beincrementally raised a set amount each time a pick is completed.However, in the present instance the reed is raised an incrementalamount each time a predetermined number of picks are completed. Thepredetermined number of completed picks between movements of the reedmay be varied, but preferably the predetermined number is between 5 and20 picks, and in the present instance the predetermined number is 10picks. Once the reed is raised to the raised position shown in FIG. 6D,the width of the reed and the dents 132 through which the yarns pass arethe narrowest part used during weaving of the graft. The controller thenmaintains the reed at the raised position shown in FIG. 6D during theweaving of the narrow section 16 shown in FIG. 1.

In the above description the reed 130 is maintained at a generallyuniform height while the first section 12 is woven and then moved to asecond height and maintained at the second height while the thirdsection 16 is woven. It should be understood that the reed may be movedduring the weaving of either the first section or the third section.However, if the reed is moved during weaving of the first or thirdsections, preferably the reed is moved at a different rate than the ratethe reed is moved during weaving of the tapered section 20.

The process of forming the grafts is a continuous weaving process thatwinds the completed grafts onto a take-up roll. As the weaving of agraft is completed, the dropped yarns are added back into the weavingpattern to widen the width of the woven fabric back out to the widestsection of the graft. For instance, referring to FIG. 1, at the end ofthe weaving process, the woven section of the fabric is as narrow as thewidth of the third section 16. Warp yarns are added back into theweaving pattern so that the woven fabric is as wide as the first section12 of the graft.

The dropped yarns may be added back into the weave in a similar mannerto how the yarns are dropped from the weave as described above. In otherwords, the process for adding the dropped yarns back into the weave mayproceed by reversing the process used to drop the dropped yarns.Additionally, while the dropped yarns are added back into the weave, thecontroller controls the reed by lowering the reed to increase the widthof the dents through which the warp yarns are drawn. In other words, thedropped yarns and the reed may be controlled so that a graft is woven inreverse of the process described above. In this way, the weaving processforms a graft tapering from wide to narrow and then from narrow to wide.This process repeats for the length of the warp yarns to produce aseries grafts in which the weaving alternates between weaving the wideportion first and dropping yarns to weaving the narrow portion first andadding yarns.

Although the grafts may be woven by reversing the weaving process, inthe present instance, the grafts are all woven by weaving the widesection first as described above. After a graft is completed, thedropped yarns are added back into the fabric during a transitionportion. As the transition portion is woven, the reed 130 is loweredback into the lowered position shown in FIG. 6A. The reed 130 is loweredat a faster rate than when the reed is raised during the weaving of thetapered section. Additionally, the number of picks between adding groupsof dropped yarns back into the weave may be less than number of picksbetween dropping groups of yarns when the tapered section 20 is woven.

After the yarns are added back in so that the fabric is as wide as thefirst section 12, the weave may not be optimally uniform to provide theuniformly smooth wall surface that is desired for the graft. However, bycontinuing to weave the fabric at a generally uniform width after theyarns are added back in, the weaving process generally settles into auniformly woven fabric that provides the uniformly smooth wall surfacedesired for the graft. Accordingly, between the end of a first graft andthe beginning of the next graft, the transition section extends furtherthan the length of the woven section in which the yarns are added backinto the web.

After weaving, the grafts are trimmed and heat set. Specifically, thegraft is cut from the length of fabric that is wound on the take-uproll. The graft is trimmed to length and the tapered transition iscut-off. The result is a flattened double cloth structure with aplurality of loose warp threads protruding from the exterior wall of thefabric. The loose ends are trimmed to minimize the length of threadprotruding from the graft. The graft is also heat set to give the grafta generally cylindrical shape. Specifically, as shown in FIG. 5, thegraft may be mounted on a mandrel 150 having the desired shape of thegraft. In the present instance, the mandrel is a generally cylindricalrod having a first diameter slightly smaller than the internal diameterof the first section. The mandrel also has a frustoconical section thattapers from the first diameter to a narrower diameter similar to theinternal taper of the tapered section 20. The mandrel also has agenerally cylindrical portion having a diameter slightly smaller thanthe internal diameter of the second portion 16 of the graft 10. Whilemounted on the mandrel, the graft is heated above a transitiontemperature to set the fibers of the graft. Additionally, the fabric maybe formed of a material that shrinks when it is heated. In this way, asthe graft is heated it shrinks to form a relatively tight fit on themandrel so that the mandrel molds the graft into the desired shape. Forexample, in the present instance, the sleeve of woven fabric is slippedover a stainless steel mandrel and heated to approximately 205° F. for15 minutes. The dropped yarns are then trimmed while the graft ismounted on the mandrel. The finished graft has a generally tubular shapesuch that the cross-section of the graft is generally circular.

The process for drawing the warp yarns and controlling the position ofthe warp yarns 52, 54 may vary depending on the configuration of thegraft. However, in the present instance, the dropped yarns 60 areinterspersed among the warp yarns across the width of the fabric. Thedropped yarns are then dropped from the weave in groups. As a result,the woven fabric comprises a ring of dropped yarns spaced apart aroundthe circumference of the graft. Specifically, referring to FIG. 1, atpoint 24 a ring is formed of a plurality of fibers that protrude fromthe outer surface of the woven fabric. The protruding fibers aregenerally equally spaced apart around the circumference of the wovenfabric. At point 26 a second ring is formed where the second group offibers was dropped and at point 28 a third ring is formed where thethird group of fibers was dropped.

Example 1

Referring now to FIGS. 7A, 7B and 8, an exemplary weaving process isdescribed for forming a tubular graft such as the graft illustrated inFIGS. 1, 2 and 4. The graft is a 28 mm×16 mm graft in which the firstsection 12 is substantially cylindrical having a 28 mm diameter and thesecond section 16 is substantially cylindrical having a 16 mm diameter.The tapered section 20 tapers at a substantially uniform rate from thefirst section 12 to the second section 16.

The fabric comprised 900 warps yarns including 500 primary yarns thatwere woven throughout the length of the graft and 400 supplementaryyarns that were woven in the first section 12 and then gradually droppedin the tapered section 20. The 400 supplementary yarns were not woveninto the second section 16.

The primary yarns were spooled on a first warp beam and thesupplementary yarns were spooled on a second warp beam. The 900 warpyarns were drawn through twenty harnesses using a straight draw. The 500primary yarns were drawn through harnesses 1-8 and the 400 supplementaryyarns were drawn through harnesses 9-20. During the weaving process, thesupplementary yarns were dropped in three different groups. The firstgroup of dropped yarns was drawn through harnesses 9-12. The secondgroup of dropped yarns was drawn through harnesses 13-16 and the thirdgroup of dropped yarns was drawn through harnesses 17-20.

FIG. 8 is a diagram illustrating the sequence for the harness draw. Thediagram shows the sequence of the yarns across the width of the fabricand which harness controlled which yarns. The diagram is read from leftto right, starting in the bottom left-hand corner of FIG. 8. Referringto FIGS. 2 & 8, the first four warp yarns of the fabric were drawnthrough the first four harnesses, which are designated 110 in FIG. 2.Specifically, the first warp yarn was threaded through the first heddleof the first harness, the second warp yarn was threaded through thefirst heddle of the second harness, the third warp yarn was threadedthrough the first heddle of the third harness and the fourth warp yarnwas threaded through the first heddle of the fourth harness. Asmentioned above, the warp yarns of the front face of the double clothfabric are designated 52 in FIG. 2. The warp yarns of the back face aredesignated 54.

The following table details the sequence of drawing a section of yarnsthrough the heddle of the harnesses in a manner similar to thatdescribed above:

Ref No. (in FIG. 2) Yarn Nos. Yarn Type Harnesses 110 1-4 Base 1-4(1^(st) heddle) 120 5-8 Supplementary 9-12 (1^(st) heddle) 112  9-12Base 5-8 (1^(st) heddle) 122 13-16 Supplementary 13-16 (1^(st) heddle)110 17-20 Base 1-4 (2^(nd) heddle) 124 21-24 Supplementary 17-20 (1^(st)heddle) 112 25-28 Base 5-8 (2^(nd) heddle

The sequence of yarns continued in this fashion according to the diagramin FIG. 8. Once the draw sequence reached the right-hand edge of thediagram in FIG. 8, the sequence repeated beginning in the bottomleft-hand corner of the diagram (i.e. harnesses 1-4). The sequence ofdrawing yarns continued until all 900 yarns were drawn through thetwenty harnesses. As can be seen, the number of yarns drawn through eachharness was different. For instance, the number of yarns drawn througheach of harnesses 1-8 (the base yarns) was different than the number ofyarns drawn through each of harnesses 9-20.

FIGS. 7A and 7B are diagrams that illustrate how the harnesses werecontrolled during the weaving process. FIG. 7A provides enlarged viewsof portions of the diagram illustrated in FIG. 7B. The diagram is readstarting from the left-hand side at the lower edge. A black markindicates that the harness was raised. No mark indicates that theharness was not raised so that the harness was in a lowered position.

Starting at the bottom left, the sequence for the harness control was asfollows. For the first pick line, the 1^(st), 5^(th), 9^(th), 13^(th)and 17^(th) harnesses were raised. The remaining harnesses remainedlowered. The shuttle 125 then passed across the width of the fabricthrough the shed formed between the raised and lowered harnesses.Harnesses 1-3, 5-7, 9-11, 13-15 and 17-19 were then raised whileharnesses 4, 8, 12, 16 and 20 were lowered. The shuttle then passedacross the width of the fabric. In line three, harnesses 4, 8, 12, 16and 20 were raised while the rest of the harnesses were lowered and theshuttle then passed across the width of the fabric. In line four,harnesses 2, 6, 10, 14 and 18 were lowered while the remaining harnesseswere raised. The shuttle then passed across the width of the fabric. Theseries of these first four lines was repeated to form the first section12 of the graft shown in FIG. 1.

While the first portion 12 of the graft 10 was woven, the reed 130remained in the lowered position as shown in FIG. 6A. After the firstportion 12 of the graft was completed, the reed 130 was raised at auniform rate along the length of the tapered section 20. Specifically,the reed was raised approximately 0.75 mm every 5 picks. In this way,transverse forces were applied to the warp yarns to narrow the width ofthe fabric. Specifically, the fabric was compressed across its widthduring the weaving process to reduce the width of the fabric.

During weaving of the tapered section 20, the supplemental yarns 60 weredropped in three groups. The first group of supplemental yarns 60 weredropped at the point designated 24 in FIGS. 1, 2 and 7B. The yarns weredropped by raising harnesses 9 and 11, lowering harnesses 10 and 12 andholding harnesses 9-12 in the respective raised and lower positionswhile the remaining harnesses were raised and lowered according to thepattern in FIGS. 7A and 7B. As shown in FIG. 7B, twenty picks after thefirst group of yarns were dropped, the second group of yarns weredropped at the point designated 26 in FIGS. 1, 2 and 7B. The secondgroup of yarns was dropped by raising harnesses 13 and 15 and loweringharnesses 14 and 16 so that harnesses 9-16 were held in their respectiveraised and lowered positions while harnesses 1-8 and 17-20 were raisedand lowered according to the pattern shown in FIGS. 7A and 7B. Twentypicks after the second group of yarns were dropped, the third group ofyarns was dropped at the point designated 28 in FIGS. 1, 2 and 7B. Thethird group of yarns were dropped by raising harnesses 17 and 19 andlowering harnesses 18 and 20 so that harnesses 9-20 were held in theirrespective raised and lowered positions while harnesses 1-8 were raisedand lowered according to the pattern shown in FIGS. 7A and 7B.

FIG. 2 illustrates a section of fabric 40 woven according to the processdescribed above in Example 1. However, for illustrative purposes, thefabric is shown at a constant width, as if the reed 130 was not raisedduring the weaving process in which the yarns were dropped.

In FIG. 2, the front face was woven from warp yarns 52 and pick yarns72. The back face was woven from warp yarns 54 and pick yarns 70. Thefirst group of dropped yarns 60 was dropped after the pick yarn at 24.The second group of dropped yarns 60 was dropped after the pick yarn at26. The loose ends of the yarns dropped from the front face aredesignated 62 a, 64 a. The loose ends of the yarns dropped from the rearface are designated 62 b, 64 b.

Since the loose ends of the dropped yarns 60 were not woven with thepick yarns, the loose ends overlie the pick yarns in the fabric becausethe harnesses for the dropped yarns of the front face remained in theraised position and the harnesses for the dropped yarns of the back faceremained in the lowered position as shown in FIG. 7B. In this way, allof the loose ends protrude from the outside of the woven tube.Alternatively, the loose ends may extend into the inside of the woventube by reversing the drop pattern by altering the sequence ofcontrolling the raising and lowering of the warp yarns.

FIG. 2 is only a fragment of the overall width of the fabric 40. Thefragment shows twenty-six of the nine hundred warp yarns that formed thegraft. The yarn sequence for the rest of the fabric followed the patternset forth in FIGS. 7A and 7B. As shown in FIGS. 2-3, the result was afabric having a plurality of yarns dropped from both faces of the fabricwith the dropped yarns being spaced out across the width of both sidesof the fabric. Therefore, the dropped yarns were spaced out around thecircumference of the graft. The dropped yarns are bounded on either sideby warp yarns that remain in the woven fabric. Transverse forces appliedalong the direction of the pick yarns during the beating process reducethe distance between adjacent warp yarns in the woven fabric after thewarp yarns were dropped.

Example 2

Referring now to FIG. 9, a second graft is designated generally 210. Thegraft 210 is a bifurcated graft having a body 212 that bifurcates toform two branches 216, 218. The body 212 is generally cylindrical andtapers at tapered section 214 from a first diameter to a smaller seconddiameter. From the reduced diameter end, the graft branches into thefirst and second branches 216, 218.

As can be seen in FIG. 9, during weaving of the tapered section 214 aplurality of the warp yarns are dropped around the graft so that thedropped yarns protrude from the surface of the graft. As in thepreviously described graft 10, the dropped yarns of the bifurcated graft210 are spaced apart around the circumference of the graft.

The bifurcated graft 210 can be utilized in a variety of applications.For instance, the bifurcated graft was formed as a woven stent graft.The body 212 is a 36 mm aortic portion and the two branches 216, 218form two 14 mm iliacs. The graft 210 is woven with 1/40/27/12Z PETfilament in a plain weave construction. The aortic region 212 is adouble-cloth tube that tapers to the two narrower double-cloth tubes.The aortic section has 1122 warp yarns, a plurality of which are droppedfrom the weave pattern when weaving the tapered section 214. Inparticular, the warp yarns were controlled so that ninety-four warpyarns were dropped three times during the weaving of the taperedsection. Fifty picks after the first group of yarns was dropped, thesecond group of yarns was dropped. Fifty picks after the second group ofyarns was dropped, the third group of yarns was dropped.

During weaving of the tapered section 214, the fabric was also narrowedby raising a tapered reed through which the warp yarns were drawn. Thereed was raised to taper the fabric 0.767 mm narrower every 10 picks ofthe tapered section weave. The dropped yarns were dropped evenly inpairs around the circumference of the tapered section 212. As a resultof dropping the warp yarns, the two branches 216, 218 were woven with420 warp yarns each. The graft is seamless because the shuttles wove theweft yarns around the tubular graft and each of the branches to form acontinuous fabric structure.

As with the first example described above, the bifurcated graft 210 waswoven on a dobby shuttle loom using twenty harnesses. Although a dobbyloom was used, it should be understood that other looms could be used tocontrol the weaving process as described above. For instance, a jacquardloom could be used to control the weaving pattern.

The loom used three shuttles to weave the fill yarns. The first shuttlewove fill yarns around the entire circumference of the body 212 and thetapered section 214. A second shuttle wove fill yarn around the entirecircumference of the first branch 216 and a third shuttle wove fill yarnaround the entire circumference of the second branch 218. The warp yarnsfor the fabric were fed from three beams: a first beam for the warpyarns forming the first branch 216; a second beam for the warp yarnsforming the second branch 218; and a third beam for the warp yarns to bedropped during weaving of the tapered section.

As in the first example, harnesses 1-8 were used for warp yarns thatwere woven through the entire length of the graft. More specifically,harnesses 1, 3, 5 and 7 were used to control the warp yarns that formedthe first branch 216. Harnesses 2, 4, 6 and 8 were used to control thewarp yarns that formed the second branch 218. Harnesses 9-20 were usedto control the warp yarns that were dropped during weaving of thetapered section 214.

The ratio between the total number of warp yarns in the body 212 and thetotal number of warp yarns in the combination of the two branches 216,218 was calculated to determine the number of warp yarns drawn versusthe number of warp yarns dropped. The calculated value for this ratiowas multiplied by four to determine the number of warp yarns in thedraw. For instance, if the ratio of total warp yarns used to the numberof warp yarns dropped would be 3 to 1 then the number of warp yarnsdrawn to warp yarns dropped would be 12:4. If the ratio is 4 to 1, thenumber of warp yarns woven to warp yarns dropped would be 16:4. Similarto the first example, the warp yarns are drawn together with the droppedyarns so that the dropped yarns are interleaved evenly across the faceof the fabric in groups of four, where two yarns of each group form thefront face and two yarns of each group form the back face of the fabric.The base warp yarns formed the two branches 216, 218. In other words,the base yarns are woven in the fabric along the entire length of thegraft.

The bifurcated graft was woven from 1122 warp yarns and 282 warp yarnswere dropped when weaving the tapered section 214. Accordingly, usingthe ratio of 12:4 the following table details the sequence of drawing asection of yarns through the heddles of the harnesses in a mannersimilar to that described above for Example 1:

Yarn Nos. Yarn Type Harnesses 1-4 Base 1, 3, 5, 7(1^(st) heddle) 5-8Base 1, 3, 5, 7(2^(nd) heddle)  9-12 Base 1, 3, 5, 7(3^(rd) heddle)13-16 Supplementary 9-12 (1^(st) heddle) 17-28 Base 1, 3, 5, 7 repeated3 times using heddles 5-8 29-32 Supplementary 13-16 (1^(st) heddle)33-44 Base 1, 3, 5, 7 repeated 3 times using heddles 9-12 44-48Supplementary 17-20 (1^(st) heddle)  49-528 Base/supplemental Repeatpattern above 10 more times 529-540 Base 1, 3, 5, 7 (repeat three times)541-544 Supplemental 9-12 545-556 Base 1, 3, 5, 7 (repeat three times)557-560 Supplemental 13-16 561-572 Base 2, 4, 6, 8 (repeat three timesusing heddles 1-3) 573-576 Supplemental 17-20 (1^(st) heddles) 577-588Base 2, 4, 6, 8 (repeat three times using heddles 4-6) 589-592Supplemental 9-12 593-604 Base 2, 4, 6, 8 (repeat three times usingheddles 9-12) 605-608 Supplemental 13-16 609-620 Base 2, 4, 6, 8 (repeat3 times using heddles 13-15) 621-624 Supplemental 17-20  625-1104Base/supplemental Repeat pattern above 10 times for yarns 561-6241105-1122 Base (2, 4, 6, 8) repeat 4 times

The tapered reed was maintained at a generally constant position whileweaving the body 212 as a substantially cylindrical tube at 150 picksper inch. After pick 1000, the reed was raised every ten picks as thenext 200 picks were woven. At pick 1050 the warp yarns from harnesses9-12 were dropped out of the weave pattern. At pick 1100 the warp yarnsfrom harnesses 13-16 were dropped out of the weave pattern. At pick 1150the warp yarns from harnesses 17-20 were dropped out of the weavepattern. At pick 1201 the pattern started weaving the first and secondbranches 216, 218. The shuttle used to weave the weft yarns with thewarp yarns for the body 212 was discontinued. Instead, the secondshuttle wove weft yarns around the warp yarns of harnesses 1, 3, 5, 7and the third shuttle wove weft yarns around the warp yarns of harness2, 4, 6, 8.

Similar to the first example, the warp yarns dropped from the weavingpattern were dropped by raising or lowering the respective warp yarnsand maintaining the dropped yarns in a raised or lowered position whilecontinuing to weave the base warp yarns.

At pick 6001 the weaving for the graft is completed and the droppedyarns were incrementally added back into the weaving pattern while thereed was lowered to widen the width of the reed where the warp yarnswere drawn through the reed. In the present example, the dropped yarnswere added back into the weave pattern twice as fast as the yarns weredropped.

After the graft was woven, the fabric was mounted onto a stainless steelmandrel having the shape of the finished bifurcated graft. The fabricwas heated to 205 degrees Fahrenheit for 15 minutes while the fabric wasmounted on the mandrel. After heating, the dropped ends protruding fromthe surface of the fabric were trimmed.

It will be recognized by those skilled in the art that changes ormodifications may be made to the above-described embodiments withoutdeparting from the broad inventive concepts of the invention. It shouldtherefore be understood that this invention is not limited to theparticular embodiments described herein, but is intended to include allchanges and modifications that are within the scope and spirit of theinvention as set forth in the claims.

We claim:
 1. An implantable woven graft, comprising: a first tubularsection wherein the first section comprises a fabric woven from aplurality of base yarns and a plurality of supplemental yarns, whereinthe first section has a first diameter and a number of warp yarns perinch; a frustoconically-shaped hollow tapered section having a firstdiameter that is similar to the first diameter of the first tubularsection, wherein the tapered section comprises a fabric woven from thebase yarns forming the first tubular section and a plurality of thesupplemental yarns, wherein the plurality of supplemental yarns aredropped from the weave pattern in the tapered section so that ends ofthe plurality of supplemental yarns protrude from the surface of thetapered section, wherein the protruding yarns are spaced apart from oneanother around the circumference of the tapered section and wherein thenumber of warp yarns per inch at the second diameter is similar to thenumber of warp yarns per inch at the first diameter.
 2. The implantablewoven graft of claim 1 wherein the hollow tapered section are droppedalong a single pick line so that ends of the protruding yarns are spacedapart around the circumference along the pick line.
 3. The implantablewoven graft of claim 2 wherein a second group of supplemental yarns aredropped from the weave pattern in the tapered section so that ends ofthe second group of supplemental yarns are spaced apart around thecircumference of the tapered section.
 4. The implantable woven graft ofclaim 3 wherein the second group of supplemental yarns are dropped fromthe weave pattern along a second pick line spaced apart from the pickline at which the plurality of supplemental lines are dropped.
 5. Theimplantable woven graft of claim 2 wherein the protruding ends of thedropped yarns form a ring circumscribing the tapered section.
 6. Theimplantable woven graft of claim 1 wherein the number of warp yarns perinch at the second diameter is substantially similar to the number ofwarp yarns per inch at the first diameter.
 7. The implantable wovengraft of claim 6 wherein the number of warp yarns per inch at the seconddiameter is within 20% of the number of warp yarns per inch at the firstdiameter.
 8. The implantable woven graft of claim 6 wherein the numberof warp yarns per inch at the second diameter is within 10% of thenumber of warp yarns per inch at the first diameter.
 9. The implantablewoven graft of claim 6 wherein the number of warp yarns per inch at thesecond diameter is within 5% of the number of warp yarns per inch at thefirst diameter.